1. Field of the Invention:
The present invention relates to current sources for use in semiconductor modules, and in particular to such sources which are integratable on the semiconductor chip and which are capable of producing impressed currents of minimal current magnitude and of brief duration, such as currents particularly suitable for use for read-out amplifiers in dynamic MOS memory modules.
2. Description of the Prior Art and Other Pertinent Patents:
In integrated semiconductor modules small currents are required at many points in the circuit such as, for example, for setting reference levels. Such currents are generally only required briefly and thus must not only be of small magnitude but also of brief duration. Such currents must also be able to be impressed at various points in the circuit exhibiting a number of different potentials.
The conventional method and apparatus for generating such small currents utilize elements having high resistance, for example, elements having long narrow diffusion paths, polysilicon paths, long, narrow MOS transistors, or by means of a series connection of a number of small transistors. All of the above-mentioned elements require a relatively large surface area on the chip, and moreover, because of the requirement that the element have a width which is exceedingly small in comparison with the length of the component, the components are difficult and expensive to manufacture due to the necessity of maintaining precise tolerances.
Further, if the various potentials at the circuit points at which the currents are introduced change during operation of the circuit, a regulated current source is required. Current sources utilizing conventional elements can only be regulated in a complicated expensive manner, which required additional use of chip surface area.
A read-out amplifier circuit for a dynamic MOS memory is described and claimed in German No. OS2623219, corresponding to U.S. Pat. No. 4,119,870 issued on Oct. 10, 1978. The circuit disclosed therein is divided into two portions, a read-out amplifier portion, and a function generator for generating a suitable control pulse for operating the amplifier. The function generator consists basically of a discharge circuit and an invertor circuit, and utilizes a number of field effect transistors thereby requiring a relatively large integration space on the chip.